Rewiring RadioShack 273-1426 stepdown(220v/110v) transformer "puzzle"

Thread Starter

arishy

Joined Apr 26, 2014
107
To avoid wasting your time. I will give you the details of the trans itself to see if it working or not.
If it is NOT working; simply ignore the post.
The trans has 3 wires ONLY. It means it is auto trans. ( correct???)
The three wires are Black, Blue and Red
Black-Blue 2.5 ohm...... side note: the device has a led !!! to indicate power on
Black-Red 150 ohm
Blue-Red 150 ohm

If I apply 220v to black-Red it gets very hot

Normal trans for 220/110 the primary reads 500-1500 ohm
This is the "first" part of the puzzle
 

ericgibbs

Joined Jan 29, 2010
15,338
hi a,
Puzzling.?
Are there any signs of a 4th wire being attached at some time.?
Does it smell 'burnt'.?
I wonder if it is a 'choke' inductor.?
E
radioshack.png
 

Thread Starter

arishy

Joined Apr 26, 2014
107
Let me reveal the second part of the puzzle:
There is a wire between the 220 v L ( it can be N it depends how you plug the 220v, AND the LIVE pin of the 110 )
I hope this helps

No burning YEY!!!!!
 

MisterBill2

Joined Jan 23, 2018
11,579
I do not believe the drawing. I am guessing that you measured with an analog ohm meter and that the difference between 150 and 152 is hard to see.
So I have a safe suggestion, which is to borrow from someplace a low voltage transformer, six volts out or possibly as much as 24 volts AC out. Then apply that voltage between the red and blue wires, and measure the voltage between the black and blue wires. I am guessing that it will be about the same as the applied voltage. between the red and blue. \
What wires was the LED (or is it neon) indicator connected to? If the applied voltage gets connected to the low voltage side then the other side will get twice as much.
 

MaxHeadRoom

Joined Jul 18, 2013
24,980
Using a similar approach, measure the lowest resistance pair, apply a small AC voltage and measure the third from each, you will be able to tell the correct phasing relationship between windings.
 

MisterBill2

Joined Jan 23, 2018
11,579
Shorted windings is certainly a possibility, I had presumed that the device was not defective. That may have been a bad guess. It would certainly explain the confusing information. It should be possible to open te paper and look, and there are some shorted-turn checks that are easy to do, but I don't recall exactly what they are. Something about a DC inductive kick.
 

Thread Starter

arishy

Joined Apr 26, 2014
107
The Radio Shack 273-1426 is a 220v to 110v converter transformer in a case:

View attachment 255140
Where did you get the transformer? Did you remove it from the case?
Wiring diagram similar to this.
View attachment 255144

2.5 ohms between blue and black seems to indicate that winding is shorted.
I got it from RadioShack (some time ago) And it was working. And yes I disassembled it. I do not recall the reason.
Your drawing makes sense to me. The only exception is the N line. In the casing, there is a wire from 220 pin to the live L of the 110 v. As you know the US 110 plug is "clear" in distinguishing L from N. The short one is L and the Long one is N
What is strange ( part of the puzzle) is the EU plug ( two pins) is very happy to deal with both L and N ;
So, as a result, the L in 110 can be N; if I plug it in 220 the "other way"
Finally the short . If Black-Blue ( 2.5 Ohm) is short then the trans is defective. It should read 150 Ohm, and the puzzle is solved
 

Thread Starter

arishy

Joined Apr 26, 2014
107
I do not believe the drawing. I am guessing that you measured with an analog ohm meter and that the difference between 150 and 152 is hard to see.
So I have a safe suggestion, which is to borrow from someplace a low voltage transformer, six volts out or possibly as much as 24 volts AC out. Then apply that voltage between the red and blue wires, and measure the voltage between the black and blue wires. I am guessing that it will be about the same as the applied voltage. between the red and blue. \
What wires was the LED (or is it neon) indicator connected to? If the applied voltage gets connected to the low voltage side then the other side will get twice as much.
I love your suggestion. I will do it today and come back to you. The LED is LED not neon. And in my naive thinking, I thought the reason for the 2.5 ohm "coil" is to feed the LED. Far out.!!!!!
 

Thread Starter

arishy

Joined Apr 26, 2014
107
Using a similar approach, measure the lowest resistance pair, apply a small AC voltage and measure the third from each, you will be able to tell the correct phasing relationship between windings.
The million-dollar question here is: the 2.5 ohm DOES NOT INDICATE A SHORT ????????? I will do all the tests and come back
 

Thread Starter

arishy

Joined Apr 26, 2014
107
Input voltage 11.3v ac ( Red-Blue) No Load
Input Voltage 10.94 ac ( Red-Blue) with Load
Output Voltage( Across Black-Blue) 33 Mvolt ( is that SHORT ?????)
 

MisterBill2

Joined Jan 23, 2018
11,579
It certainly indicates a fault, since the voltage ought to be about equal to the
Input voltage 11.3v ac ( Red-Blue) No Load
Input Voltage 10.94 ac ( Red-Blue) with Load
Output Voltage( Across Black-Blue) 33 Mvolt ( is that SHORT ?????)
It indicates a fault because the voltage across the other side of the 2:1 stepdown transformer should be about the same as the voltage across the other side. So there is a fault of some kind.
 

MisterBill2

Joined Jan 23, 2018
11,579
Since this product is an autotransformer with a 2:1 step-down ratio, the number of turns in each section should be the same, or fairly close, even if the resistance is different. Thus the inductance for each segment should be close. And given that it is not, the only conclusion is that much of the one section is short circuited. It should be possible to take the laminations apart and then remove the covering very gently and carefully examine the actual winding.
With careful work you can unwind the wire and find the short circuit location. My guess is that it is in the inner section closer to the core, since that segment has the least cooling. But that is only a guess.

And now I am thinking that it was taken apart previously because it stopped functioning correctly.
 

Thread Starter

arishy

Joined Apr 26, 2014
107
.... because it stopped functioning correctly.
If you look at the beginning of the post, you will see how I am sensitive to such issues.
And of course, I agree with you on Black-Blue it should be 150 ohms.
You have been of great help.
The 3 wire Trans was the trigger to put time and investigate, but I needed your help and you all did.
 
Top